Brake component, disc brake, drum brake, and method for manufacturing a brake component

ABSTRACT

Abstract of Disclosure 
     Brake member where the occurrence of brake squeal when a fluctuating load is applied  onto the brake member is reduced by way of a brake member or arrangement that includes a backing plate carrying a brake lining which exhibits at least one contact surface and side surfaces surrounding that contact surface and in which the side surfaces are connected to the contact surface and to the backing plate.  The contact surface is adapted to exhibit an edge area surrounding the contact surface and in which at least a portion of the edge area exhibits a local deformation stiffness in a direction vertical to a plane through the contact surface which differs, at most, fifteen percent from the deformation stiffness in a central area in the interior of the contact surface.  Utilization of this brake member is equally applicable in disc- and drum-style brake arrangements that can suffer from the occurrence of brake squeal when applying a fluctuating load onto the brake member.

Cross Reference to Related Applications

[0001] The present application is a continuation of InternationalApplication No. PCT/SE01/01395, filed 20 June 2001, published in Englishpursuant to PCT Article 21(2) and which claims priority to SwedishApplication No. 0002565-0 filed 6 July 2000. Both applications areexpressly incorporated herein by reference in their entireties.

Background of Invention

[0002] TECHNICAL FIELD: The present invention relates to a brake memberor arrangement that includes a backing plate carrying a brake liningwhich exhibits at least one contact surface and side surfacessurrounding that contact surface and in which the side surfaces areconnected to the contact surface and to the backing plate. Moreparticularly, the invention relates to a brake member where theoccurrence of brake squeal can be reduced by means of the design of abrake lining, particularly by design of the side surfaces of the brakelining.

[0003] TECHNICAL BACKGROUND: When engaging the brakes of a vehicle,sometimes so called brake squeal is created. This effect is somethingthat occurs both where disc and drum brakes are concerned. Typicalfrequencies of this noise are around a few kHz and within thesensitivity range of human hearing. The squeal noise that is produceddecreases as the distance increases from the sound source, but can stillbe approximately 140 dB when close to the braking device. Most peoplewill appreciate that city buses which stop at frequent intervals withindensely populated areas, can be particularly disturbing. One frequentreason for complaint on new private cars, lorries and buses is brakesqueal, including in association with ABS-braking systems. Even if brakesqueal does not influence the braking power, and in turn safety, theproblem is still of great importance because it is annoying to thecustomer, and therefore merits solution.

[0004] The problem of brake squeal has been analyzed many times, andmany different solutions have been tested. For example, it has beentried to dimension the components included in brake systems in order toobtain a changed natural frequency of the system, but these attemptshave not been able to reduce the occurrence of brake squeal in brakingsystems.

[0005] For example, US 5145037 discloses a disc brake where theoccurrence of brake squeal is intended to be reduced by means ofbeveling end regions of the brake disc within a region, the extension ofwhich is dependent on the width between claws included in a brake yokecarrying a backing plate where the brake lining is arranged.

[0006] Furthermore, from GB 2143919 a disc brake is known where brakesqueal is intended to be reduced by means of designing a backing plateincluded in the disc brake with an inclination in relation to the brakedisc included in the disc brake.

[0007] Even if the above-mentioned suggestions, in certain predeterminedconditions, are instrumental in reducing the occurrence of brake squeal,these solutions do not reduce the occurrence of brake squeal whenapplying a fluctuating load onto the brake member.

Summary of Invention

[0008] An object of the present invention is to provide a brake memberwhere the occurrence of brake squeal when a fluctuating load beingapplied onto the brake member is reduced. This object is achieved bymeans of a brake member or arrangement that includes a backing platecarrying a brake lining which exhibits at least one contact surface andside surfaces surrounding that contact surface and in which the sidesurfaces are connected to the contact surface and to the backing plate.The contact surface is adapted so that it exhibits an edge areasurrounding the contact surface and in which at least a portion of theedge area exhibits a local deformation stiffness in a direction verticalto a plane through the contact surface which differs, at most, fifteenpercent from the deformation stiffness in a central area in the interiorof the contact surface.

[0009] Further objects of the invention are to provide this effect indifferent types of brake members including disc- and drum-style brakesthat can suffer from the occurrence of brake squeal when applying afluctuating load onto the brake member.

[0010] Still another object of the invention is to provide a method formanufacturing brake members where the occurrence of brake squeal whenapplying a fluctuating load onto the brake member is reduced.

Brief Description of Drawings

[0011] In the following, the invention will be described in greaterdetail with reference to the attached drawings, in which:

[0012]Fig. 1 demonstrates exemplary deformation of a known brake liningwhen subjected to an equilibrium load, a larger and a smaller load;

[0013]Fig. 2 illustrates the pressure distribution of a known brakelining when subjected to an equilibrium load, a larger and a smallerload;

[0014]Fig.3 is a perspective view of a brake lining configured accordingto the present invention;

[0015]Fig.4 is a graphical representation of deformation ratio as afunction of the inclination of a side surface;

[0016]Fig.5 is a cross-sectional view of a brake member configuredaccording to the present invention; and

[0017]Fig.6 is a cross-sectional view of an alternative embodiment of abrake member configured according to the invention.

Detailed Description

[0018] As mentioned hereinabove, the phenomenon of brake squeal has beenwell studied; an example of this is found in the article entitled "Anassumed Modes Method Approach to Disc Brake Squeal Analysis" in theSociety of Automotive Engineers, 1999-01-1335 by Hulten and Flint.Therein, it is explained that, as a result of the rotational symmetry ofa brake member such as a brake disc, there are two modes at each naturalfrequency of the brake member. When a pair of modes exists for a naturalfrequency, a wave can propagate through the brake member if excitationenergy is supplied, wherein noise, so-called brake squeal, may arise.When a brake lining connects brake disc, alternatively brake drum, andbrake lining, the connected modes are divided into separate naturalfrequencies of the system. Non-conservative forces, such as for examplefrictional forces, tend to connect these separate modes and join theminto a common natural frequency in which brake squeal may arise.Accordingly, in order to prevent the creation of brake squeal, thesystem has to be designed such that a separation of a set of modes thatprimarily exhibit natural frequencies between 1 and 15 kHz can bemaintained. The connection, and thereby the occurrence of brake squeal,can occur for a number of different natural frequencies and is dependenton the interaction between brake lining and brake member, includingeither disc or drum configurations. In order to enable the design of abrake member where the risk of occurrence of brake squeal is reduced formost natural frequencies, preferably all natural frequencies within theabove-mentioned interval, it is of importance that the interactionbetween brake lining and disc or drum takes place in a predictable way.

[0019] Furthermore, in connection with the invention, studies concerningthe contact of the brake lining with the brake disc or brake drum havebeen performed. Fig. 1 shows a symbolic representation of a known brakemember 1 which interacts with a brake disc 2. The brake member includesa brake lining 3 and a backing plate 4. The brake lining 3 exhibits afirst and a second contact surface 5a, 5b, which are intended to pressagainst the brake disc 2 or, whenever applicable, against a brake drum.Furthermore, the brake lining 3 exhibits a groove 6 that delimits thecontact surface 5a from the contact surface 5b.

[0020] During the working life of the brake lining 3, it will be worndown so that the brake lining forms a flat surface when a certain forceis applied onto the brake lining by, for example, braking cylinders. Theinitial condition (an equilibrium condition) is shown in Fig. 1 with acontinuous line. Fig. 2 schematically illustrates the pressuredistribution across the contact surfaces during the run-in conditionwhere the contact surface or surfaces of the brake lining are flat as isshown by the continuous line.

[0021] The left part of Fig. 1 shows deformation of the brake lining 3,with dashed lines, when it is pressed against a brake disc 2 or,whenever applicable, a brake drum with a force which is smaller than theparticular force resulting in the above-mentioned flat equilibriumcondition. In this case, the contact surface of the brake disc isdisplaced from the initial position 7 into a second position 7'.Furthermore, in exaggerated magnification, it is shown how the surfaceof the brake lining is deformed into a shape that has been indicatedwith dashed lines when subjected to a smaller load. Since the localdeformation stiffness of the brake lining varies across the surface,different contact forces are created across the surface of the brakelining by a force that differs from the particular force that createsthe equilibrium condition. Here, local deformation stiffness means thespring constant in a locally delimited area in the direction of thenormal to the contact surface. Studies have shown that the springconstant of a homogenous material is lower at an edge region havingvertical side surfaces than in regions having inclined side surfaces orin an inner region at a distance from the edge of the homogenousmaterial. This means that the spring constant at the groove 6 located inthe brake lining 3 exhibits a lower deformation stiffness than in aninner region of the brake lining. Furthermore, the brake lining 3exhibits a higher deformation stiffness at the beveled flanks 8 than inthe inner region of the brake lining. This results in the brake liningbulging outwards at the region (I) located closest to said groove 6, andbulging inwards at the region (III) located closest to the beveled edge8, when subjected to the smaller load.

[0022] The left part of Fig. 2 shows the pressure distribution acrossthe brake lining 3, with dashed lines, when the brake lining is loadedwith a smaller load than the abovementioned certain equilibrium force.From the explanation above, it is evident that the pressure within theregion (I) is higher than within the region III when a smaller load thanthe equilibrium load is applied onto the brake lining. The pressuredistribution at the abovementioned certain force is shown withcontinuous lines.

[0023] The right part of Fig. 1 shows deformation of the brake lining 3,with dashed lines, when the brake lining is pressed against the brakedisc 2 or, whenever applicable, a brake drum, with a force exceeding theabove-mentioned certain force resulting in the flat equilibriumcondition. In this case, the contact surface of the brake disc isdisplaced from the initial position 7 into a third position.Furthermore, in exaggerated magnification, it can be seen how thesurface of the brake lining is deformed into a shape that is indicatedwith dashed lines when subjected to a larger load. Since the localdeformation stiffness of the brake lining varies across the surface,different contact forces are created across the surface of the brakelining as a result of a force that differs from the above-mentionedcertain force resulting in said equilibrium condition. Also in thiscase, the spring constant at the groove 6 located in the brake lining 3exhibits a lower deformation stiffness that in an inner region of thebrake lining, and the brake lining 3 exhibits a higher deformationstiffness at the beveled flanks 8, 9 than in the inner region of thebrake lining. This results in the brake lining bulging inwards at theregion (I) located closest to the groove 6, and bulging outwards at theregion (III) located closest to the beveled edge 8, when subjected tothe larger load.

[0024] The right part of Fig. 2 shows the pressure distribution acrossthe brake lining 3, with dashed lines, when the brake lining is loadedwith a larger load than the abovementioned certain force. From theexplanation above, it is evident that the pressure within the region (I)is lower than within the region (III) when a larger load than theequilibrium load is applied onto the brake lining. The pressuredistribution with the above-mentioned certain force is shown withcontinuous lines.

[0025] As a result of these shape and pressure changes that occur whenapplying different pressure forces to the brake lining, it is madeconsiderably more difficult to design brake linings where the risk ofconnecting a plurality of separated modes can be reduced.

[0026] Accordingly, an object of the present invention is achieved bymeans of providing a brake system where a brake lining exhibits acontact surface having an edge area surrounding the contact surfacewherein at least a portion of the edge area exhibits a local deformationstiffness in a direction vertical to a plane through the contact surfacewhich differs fifteen percent (15%) at most from the deformationstiffness in a central area in the interior of the contact surface. Bymeans of this design, a substantially more constant pressure is createdacross the brake lining when subjected to different loads.

[0027]Fig. 3 shows a perspective view of a brake member 1 according tothe invention. The brake member is arranged in a general way forinteracting with a brake disc or a brake drum. Examples of suchinteraction and included elements necessary in order to provide afunctioning braking device are well known. Exemplary arrangements arefound in US 5,145,037 and GB 2 143 916, each of which are expresslyincorporated by reference for purposes of disclosure of sucharrangements, and which constitute an example of a disc brake wherebrake members according to the invention can be utilized. SE 504 272provides an example of a drum brake where brake members according to theinvention can be utilized.

[0028] The brake member 1 includes a brake lining 3 and a backing plate4. Preferably, the brake lining 3 and backing plate 4 are designed inone piece. Alternatively, the brake lining 3 can be attached to thebacking plate 4 in any way known to the skilled person. The brake lining3 constitutes a wear surface when the brake member is used for braking,and the backing plate distributes the pressure force from brakingcylinders (not shown) to the brake lining when the brake member isutilized in a brake device. One example of the design of a brake devicehaving braking cylinders can be found in US 5,145,037.

[0029] In a preferred embodiment, the brake lining exhibits a first anda second contact surface 5a, 5b which are intended to be pressed againsta brake disc or, whenever applicable, against a brake drum. It should beappreciated that such a disc or drum is not shown in Fig. 3, but wouldbe positioned above the lining 3 for pressed engagement therewith.Furthermore, the brake lining 3 in this embodiment exhibits a groove 6that delimits the contact surface 5a from the contact surface 5b. Theinvention also can be utilized with brake linings having a single wearsurface, but is particularly advantageous with brake linings havingseveral wear surfaces separated by grooves, since the edge/area-ratio ofthe contact surfaces of such brake members is usually larger.Furthermore, the contact surfaces 5a and 5b exhibit an edge area 9including a first edge area 9a surrounding the first contact surface 5aand a second edge area 9b surrounding the second contact surface 9b.According to what has been described above, the contact surfaces 5a, 5bare worn down during the life of the brake member, so that they are flatand exhibit a surface normal e_(z). The edge area is defined as the areawhere the contact surfaces 5a, 5b are connected to side surfaces 10-15.Accordingly, the side surfaces exhibit surface normals e_(s) extendingin different directions from the surface normal e_(z) of the contactsurfaces (see Figs. 5 and 6). In a preferred embodiment, the sidesurfaces include a front and a rear flank 11, 12 that are beveled. Theflanks are introduced in order to compensate for the edge effects thatarise during the force transfer from the braking cylinders to thebacking plate. According to what has been described above, the inventioncan be utilized both with brake linings designed without flanks, as wellas with brake linings designed with flanks. According to traditionaldesigns, the front and rear flanks usually are designed with a surfacenormal which is inclined approximately fifteen degrees in relation tothe surface normal e_(z) of the contact surface. In the embodiment wherea front and rear flank are arranged on the brake lining 3, said sidesurfaces include a first set of side surfaces 10, 13 extending betweensaid front and rear flanks 11, 12. Whenever applicable, said sidesurfaces further include a second set of side surfaces 14, 15 betweenwhich the groove 6 extends.

[0030]Figure 4 shows a diagram of deformation ratio as a function of theinclination of a side surface. It is assumed that areas having the samelocal deformation stiffness will have the same contact pressure when thebrake lining is subjected to different loads. Thus, the brake membershould be designed such that the local stiffness is the same across theentire contact surface of a brake lining. Accordingly, the diagram showshow the deformation ratio varies with the inclination of a side surfacein relation to the contact surface. The calculation has been performedfor flat side surfaces having a surface normal e_(s) which forms anangle between 74^(o) and 90^(o) with the surface normal e_(z) of thecontact surface. This means that the side surface forms a flat surfacethat is slightly beveled in the portion of the side surface facing thecontact surface.

[0031] The diagram further shows preferred embodiments of the inventionwhere the brake lining exhibits side surfaces that exhibit an anglebetween 78 and 86 degrees in relation to the contact surface when thedeformation ratio differs by less than approximately fifteen percent(15%). A further preferred embodiment of the invention is represented inwhich the brake lining exhibits side surfaces having an angle between 80and 84 degrees in relation to the contact surface when the deformationratio differs by less than approximately ten percent (10%). Stillanother preferred embodiment of the invention is demonstrated where thebrake lining exhibits side surfaces which exhibit an angle between 81and 83 degrees in relation to the contact surface when the deformationratio differs by less than approximately five percent (5%).

[0032]Figure 5 shows a cross-section of a brake member 1 according tothe invention. The brake member 1 exhibits a brake lining 3 and abacking plate 4. The brake lining 3 exhibits a contact surface 5a havinga surface normal e_(z). Furthermore, the brake lining exhibits a sidesurface 16, which preferably is chosen optionally from said first andsecond set of side surfaces 10, 13-15. The side surface 16 exhibits asurface normal e_(s). The surface normal of the side surface and thesurface normal of the contact surface form an angle of (90 - alpha )degrees with each other when the brake member is in an unloadedcondition. The side surface 16 and the contact surface 5a are connectedin an edge area 9. Furthermore, Figure 5 shows the brake member in acondition when subjected to a heavy load, indicated with dashed lines,wherein it can be noticed that the entire contact surface 5a has beensubjected to a parallel displacement into a new position 5a'. A paralleldisplacement under constant pressure across the surface is achieved bymeans of giving the edge area the same local deformation stiffness as acentral area 17 in the interior of the contact surface. The central area17 in the interior of the contact surface can be defined as all pointson the contact surface which are at a distance from an edge 9 whichexceeds the thickness H, preferably three times the thickness of thebrake lining 3, as measured in the direction of the surface normal e_(z)of the contact surface.

[0033] A brake member according to the present invention is achievedwhen configured to have side surfaces designed in an inclined manner andwith a limited variation of local deformation stiffness between edge andinterior of the contact surface 5a of the brake lining 3. In the exampleshown in Figure 5, the side surface 16 is designed to be flat, whichmeans that the edge will be stiffened to the same degree independent ofhow much the lining is worn down.

[0034]Figure 6 shows the invention according to another embodiment,where the surface normal e_(s) of the side surface 16 varies with thedistance from the backing plate 4. This embodiment can be utilized whenthe influence of the backing plate 4 on the local deformation stiffnessof the brake member 1 makes a separate compensation by means of the edgedesign necessary in order to obtain an edge area having a smalldeviation in deformation stiffness depending on the thickness andthereby the wear of the brake lining. In this case, according to apreferred embodiment of the invention, the side surface 16 is designedwith an arbitrary surface normal e_(s) within the main portion 18 of awear area 19 within the side surface 16, which surface normal e_(s)makes an angle between 78 and 86 degrees with an arbitrary surfacenormal e_(z) within the main portion of the contact surface when thebrake member is in an unloaded condition. In the present context, "mainportion" should be understood to mean a predominant portion of at leastfifty percent or more of the total article, area or portion sodescribed. The wear area is defined as the portion of the side surfacethat is intended to be worn down during the working life of the brakemember 1. The main portion 18 of the wear area can be constituted by theentire thickness of the brake lining or a local part of this, however,preferably at least 50% of the thickness of the brake lining when thebrake lining is in an original condition. Preferably, the side surfaceis designed with a surface normal e_(s) which makes a larger angle withthe surface normal e_(z) of the contact surface at portions of the sidesurface which are located close to the backing plate 4 than at portionswhich are located close to the contact surface 5a.

[0035] The brake lining and the backing plate are made of materials thatare well known to the skilled person.

[0036] The invention also relates to a method for manufacturing a brakemember including a backing plate carrying a brake lining which exhibitsat least one contact surface and also side surfaces surrounding the atleast one contact surface. The side surfaces are connected partly to thecontact surface and partly to the backing plate, wherein the contactsurface is designed with an edge area surrounding the contact surface,wherein at least a portion of the edge area exhibits a local deformationstiffness in a direction vertical to a plane through the contact surfacewhich differs fifteen percent (15%) at most from the deformationstiffness in a central area in the interior of the contact surface.

[0037] In a preferred embodiment of the method, a local deformationstiffness differing ten percent (10%) at most is obtained.

[0038] In a further preferred embodiment of the method, a localdeformation stiffness that differs 5 % at most is obtained.

[0039] In a preferred embodiment of the method of the invention, thesurfaces are designed for allowing the edge area to exhibit thedeformation stiffness. In a further preferred embodiment of the method,the side surfaces are designed with an arbitrary surface normal withinthe main portion of a wear area within the second set of side surfaceswhich makes an angle to an arbitrary surface normal within the mainportion of the contact surface which is between 78 - 86 degrees,preferably between 80- 84 degrees, and even more preferably 81 - 83degrees when the brake member is in an unloaded condition.

[0040] According to the invention, a method where the brake member isformed from a material having a varying deformation stiffness, and thevariation is arranged to allow a portion of the edge area to exhibit alocal deformation stiffness in a direction vertical to a plane throughthe contact surface which differs fifteen percent (15 %) at most fromthe deformation stiffness in a central area in the interior of thecontact surface, can also be utilized. In a preferred embodiment, thedeformation stiffness differs ten percent (10%) at most, and preferablyfive percent (5%).

[0041] The invention can be utilized for different types of disc anddrum brakes which are well known to the skilled person.

Claims
 1. A brake member comprising: a backing plate carrying a brake lining, said brake lining having at least one contact surface and side surfaces surrounding said at least one contact surface, said side surfaces being connected between said contact surface and said backing plate; and said contact surface having a surrounding edge area and at least a portion of said edge area exhibiting a local deformation stiffness in a direction vertical to a plane through the contact surface which differs fifteen percent at most from the deformation stiffness in a central area of an interior portion of the contact surface.
 2. A brake member as recited in claim 1, further comprising: said side surfaces along said portion of said surrounding edge area having a local deformation stiffness in a direction vertical to a plane through said contact surface differing at most fifteen percent from the deformation stiffness in said central area in said interior of said contact surface.
 3. A brake member as recited in claim 1, wherein the local deformation stiffness differs ten percent at most.
 4. A brake member as recited in claim 1, wherein the local deformation stiffness differs five percent at most.
 5. A brake member as recited in claim 1, wherein the brake lining includes at least two contact surfaces separated by a groove and said portion of said edge area includes a main portion of the edge area of the contact surfaces along said groove.
 6. A brake member as recited in claim 5, wherein said groove extends between a second set of side surfaces and a surface normal within the main portion of a wear area within said second set of side surfaces makes an angle between 78 and 86 degrees with an arbitrary surface normal within the main portion of the contact surface when the brake member is in an unloaded condition.
 7. A brake member as recited in claim 6, wherein said angle measures between 80 and 84 degrees.
 8. A brake member as recited in claim 6, wherein said angle measures between 81 and 83 degrees.
 9. A brake member as recited in claim 6, wherein said second set of side surfaces within the main portion of a wear area within said second set of side surfaces are substantially flat.
 10. A brake member according to claim 9, characterized in that an arbitrary surface normal within the main portion of a wear area within said first set of side surfaces makes an angle between 78 - 86 degrees with an arbitrary surface normal within the main portion of the contact surface when the brake member is in an unloaded condition.
 11. A brake member as recited in claim 10, wherein said first set of side surfaces within the main portion of a wear area within said first set of side surfaces are designed substantially flat.
 12. A brake member as recited in claim 1, wherein the brake lining includes a front and a rear flank which are beveled, and said side surfaces include a first set of side surfaces extending between said front and rear flank, and said portion of said edge area includes the main portion of an edge of said contact surface or surfaces at said first set of side surfaces.
 13. A brake member as recited in claim 12, wherein said angle measures between 80 and 84 degrees.
 14. A brake member as recited in claim 12, wherein said angle measures between 81 and 83 degrees.
 15. A brake member as recited in claim 12, wherein said portion of the edge area includes the main portion of an edge of said contact surface or surfaces at the front and rear flank.
 16. A brake member as recited in claim 1, wherein said brake member is adapted to be utilized in a disc brake arrangement.
 17. A brake member as recited in claim 1, wherein said brake member is adapted to be utilized in a drum brake arrangement.
 18. A brake member as recited in claim 1, wherein said brake member is formed from a material having a varying deformation stiffness, and that the variation is arranged for allowing said edge area to exhibit said deformation stiffness. 